The influence of aluminium sources on the acidic behaviour as well as on the catalytic activity of mesoporous H-AlMCM-41 molecular sieves (original) (raw)
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Catalysis today, 2000
Mesoporous AlMCM-41 molecular sieves were synthesized using various aluminium sources, viz., sodium aluminate, aluminium sulphate, aluminium isopropoxide and pseudoboehmite. The influence of different aluminium sources on the framework substitution of aluminium as well as on the catalytic properties of t-butylation of phenol was studied. Among the aluminium sources, the use of sodium aluminate for the AlMCM-41 synthesis showed maximum incorporation of aluminium in the framework. Further, the catalyst also showed good catalytic activity for the chosen reaction.
Zeolites, 1993
MeAPO molecular sieves (Me: Co, Mn, and Zn) with the AFI structure type and an AIPO4-5 for reference were synthesized. The products were characterized by X-ray fluorescence, XRD, thermodielectrical analysis, NH3 adsorption, and temperature-programmed reduction (t.p.r). It was shown that the cell parameters and the adsorption volume of MeAPO-5 molecular sieves are higher than those for AIPO4-5. Thermodielectrical data are consistent with the fact that the charge of the anionic framework of the as-synthesized MeAPO-5 is compensated by (HTEA) +. T.p.r. results show that Co, Zn, and Mn are included in the molecular sieve framework of
Aluminum chloride grafted mesoporous molecular sieves as alkylation catalysts
Microporous and Mesoporous Materials, 2005
The aim of this work is to study the influence of different mesoporous molecular sieves (MMSs) type and the effect of pore diameter on MMSs silica grafted aluminum chloride catalysts and their activity in benzene alkylation by 1-dodecene. Four samples (two hexagonal and two wormhole like structures with different pore diameters) were prepared by post-synthesis grafting reaction in moisture free conditions (Schlenk technique). The physico-chemical properties were monitored by N 2 adsorption, XRD, atomic adsorption, 29 Si and 27 Al MAS NMR. Acidity data were obtained by TPD of ammonia, and FTIR of adsorbed pyridine. The alkylation of benzene is carried out in a Schlenk tube under dry conditions at room temperature. The products were analyzed by GC-MS. Grafting aluminum chloride on MMSs increases the yield of monoalkylated products.
2001
Mesoporous aluminophosphate (AIPO) and silicon substituted aluminophosphate molecular sieves (SAPO) have been synthesized using ordered array of cetyltrimethylammonium bromide as structure-directing agent at room temperature. The characteristics of these new materials are ascertained by low angle XRD, TGA, Ff-IR, SEM and DRlFf spectra. Vapour phase ethylation of toluene has been attempted over these molecular sieves as a probe reaction. The principal product is pethyltoluene in this reaction. This study also indicates more free uncondensed -OH groups in pure AI PO.
2011
AlSBA-3 mesoporous catalytic materials with different Si/Al ratios were synthesized; Al was incorporated in the mesoporous structure using the post-synthesis method. The catalysts were characterized using different techniques and methods, such as: XRD, BET, ICP, SEM microcopy, TEM microscopy and 27 Al MAS NMR. Acidic properties were estimated by adsorption–desorption using pyridine as probe molecule followed by FTIR spectroscopy. FTIR studies showed the acidic properties with aluminum incorporation; lower Si/Al ratios increase the number of acid sites. Temperature-programmed desorption of pyridine showed that AlSBA-3 has a higher number of strong acid sites compared to other mesoporous materials such as Al-MCM-41, Al-SBA-15 and Al-SBA-16. It has been observed by 27 Al MAS NMR spectroscopy, that the materials exhibit peaks with shifts of 50 ± 2 ppm and weak signal at 0 ± 2 ppm. The AlSBA-3 materials used as a catalyst showed high performance in the acid-catalyzed dehydration of isopr...
Journal of Molecular …, 2004
Mesoporous aluminophosphate (AlPO) has been synthesized hydrothermally using cetyltrimethylammonium bromide (CTAB) as structure-directing agent in the presence of tetramethylammonium hydroxide (TMAOH) at room temperature. Phosphotungstic acid, H3PW12O40 (PW) was supported on the synthesized mesoporous AlPO at various loadings viz., 10, 20 and 40wt.% to yield PW/AlPOs and characterized by XRD, TGA and FT-IR. XRD patterns confirm that HPA retains the
Journal of Materials Science, 2009
Silica-alumina covering broad range of compositions have been obtained by combined hydrolysis precipitation. These materials were characterized mainly by solid-state NMR spectroscopy. Textural properties were investigated by measurements of nitrogen sorption, and the acidity of Brønsted sites was studied by TPD and FTIR spectroscopy using ammonia as probe molecule. The catalytic performance of these materials was studied by the Brønsted acid-catalyzed acetalization reaction. New insights into the nature of the silicate compartment and the acidity of Brønsted sites of amorphous silica-alumina have been obtained. Silica-aluminas of different silica content do not represent a homologous row. They differ mainly in the connectivity of the silicate compartment. The results show that silica-alumina contain a quantitative amount of Brønsted sites. The appearance of tetrahedral Al is closely related to silica. The concentration of tetrahedral Al, and hence Brønsted acid sites, follows a volcano shape. After increasing with SiO 2 content, the site concentration reaches a maximum at 20 wt% of silica and decreases again due to the marked decrease in the total alumina content in high silica samples. Surprisingly, the catalytic activity does not follow this trend. It increases especially with high silica samples due to the interplay of acid site concentration and the strength of acid sites. The aluminosilicate compartment of high silica samples shows a high Si/Al ratio. The improved acid strength of the sites overcompensates the lower site concentration, leading to a distinctly enhanced catalytic activity.
Vapor-phase tertiary butylation of phenol over mesoporous gallosilicate molecular sieves
Catalysis letters, 2002
Isomorphously substituted GaMCM-41 molecular sieves with dierent Si : Ga ratio were synthesized and characterized systematically by various analytical and spectroscopic techniques. Temperature-programmed desorption of ammonia was used to identify the nature of acidic sites. For the ®rst time, the vapor-phase tertiary butylation of phenol reaction was carried out over protonated GaMCM-41. The catalysts showed higher (phenol) conversion and good ( para-tertiary butyl phenol) selectivity over the Al-and Fe-analogs of MCM-41. Further, the gallosilicates showed good stability both before and after the reaction compared to the aluminosilicates or ferrisilicates.
Mesoporous molecular sieves: alkylation of anisole usingtert-butylalcohol
Catalysis Letters, 2006
Mesoporous aluninosilicate Al-MCM-41 molecular sieves with Si/Al ratios 25, 50, 75 and 100 have been synthesized under hydrothermal condition and these materials were characterized by XRD, FTIR, BET and pyridine adsorption techniques. The catalytic performance was examined in the vapor phase tert-butylation of anisole with tert-butanol at the temperatures between 150 and 250 °C under atmospheric pressure. The results indicate that Al-MCM-41 (25) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). Maximum conversion of anisole is observed at 175 °C and decreased thereafter with increasing temperature. The influence of molar feed ratio, influence of temperature, WHSV and time on stream on the selectivity of products was investigated and the results are discussed.